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Title:
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The dark decay of HONO in reaction-chambers
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Author(s):
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Published by:
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Publication date:
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ECN
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1996
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ECN report number:
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Document type:
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ECN-RX--96-039
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Other
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Number of pages:
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Full text:
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22
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Download PDF
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Abstract:
The decay of gaseous nitrous acid (HONO) was studied in reaction chambersof glass and polyethylene at concentrations in air ranging from 100 ppbv to
10 ppmv and relative humidities between 50% and 80%. The initial decay was
independent of the relative humidity and could be described by a second-order
process with a rate constant of 8 (-.5) * 10"-"5 ppm"-"1.min"-"1. Only a
small amount of NO was formed, showing that the initial decay of HONO is
(heterogeneous) removal at the reactor wall. At longer residence times
decomposition of HONO into the nitrogen oxide gases was the dominant process
and equilibrium between HONO, NO, NO2 and H2O was established. The initial
heterogeneous decay was not measurably different in the two types of chambers
with their different wall surface materials. When the walls of the chambers
had been wet before experiments, the decay was up to ten times more rapid,
showing the importance of adsorbed water. Additional surface in the form of
copper oxide aerosols or NaCl droplets, present at concentrations far
exceeding ambient values, did not accelerate the decay. Whereas the rate of
decay was not measurably modified by the NaCl, HONO reacted with the droplets
by substituting of the order of 2.5% of the chloride by nitrate. This
reaction occurred when the aerosol was present as stable droplets at 80% and
as metastable droplets at 50% relative humidity. The extent of the reaction
seemed independent of the HONO concentration. A measurable reaction was
absent with dry NaCl aerosol at 30% RH. 3 figs., 13 refs.
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